Gravitational force, electric force and magnetic force are three natural forces that can act at a distance. The use of magnetic forces, such as in magnetic levitation and magnetic bearings, are growing. Many practical applications for the magnetic forces are known, such as magnetically levitated trains, magnetic gears, etc. Conventional mechanical gears that are normally used in machines also have a magnetic counterpart in the magnetic gears.
There are a number of advantages in using magnetic gears over the conventional mechanical gears. For example, mechanical gears can generate much vibration and noise during operation, whereas magnetic gears significantly reduce such vibration and noise. Furthermore, the mechanical gears need lubrication and inspection for wear and tear from time to time. Therefore, if the gears can operate in a non-contact fashion, all those problems caused by friction, wear, vibration and noise disappear. Moreover, such non-contact gears are almost maintenance-free.
Magnetic gears operate through the interaction of magnetic field set up between two magnetic gears, and torque is transmitted by their mutual attraction and repulsion due to a magnetic coupling. Most conventional magnetic gear systems are designed for the coaxial type, because large torque can be transmitted. Because the magnetic coupling is achieved by the action of an electromagnet, problems, such as winding space and control current, must also be considered. Therefore, this type of magnetic gear design becomes rather complicated.
Nevertheless, since the torque transmitted through a coaxial magnetic gear system is provided by mutual interactions involving all the magnets in the two magnetic rings, a large torque can be transmitted by the coaxial magnetic system. However, due to directional restrictions of a coaxial type of magnetic gear transmission system, non-coaxial type of magnetic gear transmission system cannot be completely replaced with the coaxial type. Furthermore, the recent advances in the material research have produced a number of powerful magnets, such as a strong magnetic compound known as neodymium iron boron (NdFeB). Therefore, non-coaxial magnetic gear systems have practical value and there is a need in the art for improved non-coaxial magnetic gear systems.